Derrick lift system of offshore structure

ABSTRACT

Disclosed herein is a derrick lift system of an offshore structure. The derrick system can improve drilling workability by enabling safe and easy height adjustment of a derrick using an adjustment unit, and can improve structural stability by lowering the center of gravity of the derrick through the height adjustment of the derrick, as occasion demands.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application Nos.10-2014-0004950 and 10-2014-0004951, filed on Jan. 15, 2014 in theKorean Intellectual Property Office, the entirety of which isincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a derrick lift system of an offshorestructure, and more particularly to a derrick lift system of an offshorestructure, which enables stable movement of a derrick in a verticaldirection in drilling operation while allowing easy adjustment of theheight or level of the derrick.

2. Description of the Related Art

With rapid industrialization and industrial development, usage ofresources such as petroleum has gradually increased and thus stableproduction and supply of oil are important issues at a national level.For this reason, there has recently been developed a drill ship withdrilling equipment economically proper to develop a minor limited oilfield or a deep sea oil field that has been untapped due to economicinfeasibility, as well as land drilling.

In conventional offshore drilling, there has been generally used a rigship designed for offshore drilling or a stationary platform that mustbe transported by tugboats, and perform drilling in a state of beinganchored at a predetermined location at sea by a mooring device. Inrecent years, however, a so-called drill ship manufactured like ageneral ship is developed to have state-of-the-art drilling equipmentand navigate under its own power, and is used in offshore drilling.

In the central region of the rig ship or drill ship provided with avariety of drilling equipment for drilling for oil, gas, and the likeunder the sea bed, a moon pool is formed such that a drill string, thatis, a riser or a drill pipe for drilling for oil, gas, etc. under thesea bed can be moved up and down.

FIG. 1 is a side view showing drilling operation of a typical drillship.

Referring to FIG. 1, a riser 3 and a drill pipe 4 are moved downwardsthrough a moon pool 2 formed at the center of the drill ship, and thendrill for seabed resources in an oil well 12 placed in a reservoir 11under the seabed 5.

The riser 3 is moved down to the sea bed 5 before moving the drill pipe4 to the oil well 12 and provides a passage through which mud returns.

With the riser 3 placed outside the drill pipe 4, the drill pipe 4 ismoved down to the oil well 12 through a sub-bottom stratum 10 along theriser 3.

Here, before the riser 3 is moved down to the seabed 5 or the drill pipe4 is moved down to the oil well 12, short risers or short drill pipesare sequentially connected to each other to form the riser 3 or thedrill pipe 4, which in turn is moved downwards.

On the seabed 5, a blowout preventer (BOP) 6 is placed to preventtransfer of abnormally high pressure along the drill pipe 4.

In the sub-bottom stratum 10, a casing 7 is secured and a drill pipe 4provided with a drill bit 9 is inserted into the casing 7 and drills forthe seabed resources.

To prevent the drill bit 9 from overheating by heat generated when thedrill bit 9 drills the ground and to facilitate drilling throughlubrication, mud 8 is inserted into the drill pipe 4. The mud escapesthrough the drill bit 9 and returns through the casing 7 and the riser3.

When the drilling operation is completed, the drill pipe 4 is moved to adrill floor through the moon pool 2, separated, and then carried to aloading place.

FIG. 2 is a view of a typical derrick structure in the related art.

Referring to FIG. 2, a typical drill ship includes an upper deck 13 anda drill floor 14 placed on the upper deck 13. A derrick 1 is placed onthe drill floor 14. Drill pipes 4 transversely loaded in a pipe loadingarea are raised and clamped by a top drive 15 and a rotary table 16.

Two or more drill pipes 4 coupled to each other are temporarily loadedin a setback area in a vertical direction, and moved downwards towardthe moon pool in drilling operation.

The derrick 1 serves to move drilling equipment such as the drill pipe 4and the like up or down to a desired location in a vertical direction bywinding or releasing a wire rope connected to the drilling equipmentthrough operation of a winch.

Generally, although the height of the derrick varies depending upondesign, the derrick 1 refers to a truss type steel tower having a heightof about 100 m. In the related art, derricks tend to be increasing insize to suit drilling operation at increasing depths.

Since a typical derrick has a fixed height, the typical derrick has ahigh center of gravity, causing very low structural stability of thehull.

To resolve such problems in the related art, Korean Patent PublicationNo. 2012-0032128 discloses a derrick elevator capable of adjusting theheight of the derrick. However, this derrick system has a problem of lowworkability due to difficulty in height adjustment of the derrick.

BRIEF SUMMARY

The present invention has been conceived to solve such problems in therelated art, and an aspect of the present invention is to provide aderrick lift system of an offshore structure which can safely andrapidly move a derrick in a vertical direction in drilling operation,and can improve structural stability by lowering the center of gravityof the derrick through the height adjustment of the derrick, as occasiondemands.

In accordance with one aspect of the present invention, a derrick liftsystem of an offshore structure includes: a base plate secured to adrill floor and having a locking groove formed on one side thereof; agearbox placed at one inner side of the base plate and coupled to adrive motor; a relay gear rotably mounted on the base plate to engagewith the gearbox; a pinion rotably mounted on the base plate to engagewith the relay gear; a post supporting a lower end of the derrick tolift or lower the derrick and provided to the other inner side of thebase plate to be perpendicularly movable, and having a rack formed onone surface thereof to engage with the pinion and a locking grooveformed on one surface thereof; a stopper mounted on the base plate andselectively inserted into the locking grooves to secure the post at alifted or lowered location; and a derrick height adjustment unit placedat one side of the base plate to align the locking grooves throughheight adjustment of the derrick.

The derrick height adjustment unit may include a mounting bracketsecured to the base plate; and a hydraulic cylinder provided to themounting bracket and adjusting the height of the derrick.

The base plate may be provided with a sensor detecting alignment of thelocking grooves.

The pinion may include a securing pin engaging with the rack, and thebase plate may be provided with a safety cylinder coupled to the stopperto selectively lock the stopper.

The base plate may be provided with a ratchet cylinder, and the ratchetcylinder may include a rod and a pivot latch rotably installed at therod. The pivot latch stops a latch jaw of the pinion selectively andlatches the pinion.

The base plate and the post may be arranged to support four lowercorners of the derrick.

According to a modification of the invention, the stopper may include aguide plate secured to a side surface of the base plate and having aguide rail formed on an upper surface thereof; a rod horizontallysecured above the guide plate; a cylinder body disposed to receive therod therein and to be locked into the locking grooves while moving alongthe rod by hydraulic force and having safety grooves formed on uppersurfaces of both ends thereof; and a safety cylinder secured to a sidesurface of the base plate and coupled into the safety grooves to preventseparation of the cylinder body from the locking grooves when thecylinder body is inserted into the locking grooves.

The cylinder body may be formed with fluid inlet and outlet ports and ahydraulic chamber, and may have safety grooves formed on upper surfacesof both ends thereof.

According to the present invention, the derrick lift system of anoffshore structure can improve drilling workability by enabling safe andeasy height adjustment of a derrick using an adjustment unit, and canimprove structural stability by lowering the center of gravity of thederrick through the height adjustment of the derrick, as occasiondemands.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become apparent from the following description ofembodiments given in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a side view showing drilling operation of a typical drillship;

FIG. 2 is a view of a typical derrick structure in the related art;

FIG. 3 is a side view of a derrick lift system of an offshore structureaccording to one embodiment of the present invention, viewed from portside;

FIG. 4 is a side view of the derrick lift system of an offshorestructure according to the embodiment of the present invention, viewedfrom starboard side;

FIG. 5 is a side view of the derrick lift system of an offshorestructure according to the embodiment of the present invention, viewedfrom aft side;

FIG. 6 is a side view of the derrick lift system of an offshorestructure according to the embodiment of the present invention, viewedfrom a forward side;

FIG. 7 is an enlarged view of a main part of the derrick lift system ofFIG. 3;

FIG. 8 is a plan view of the derrick lift system of FIG. 7;

FIG. 9 is an enlarged view of a main part of the derrick lift system ofFIG. 7;

FIG. 10 is a sectional view of the derrick lift system taken along lineI-I of FIG. 3;

FIG. 11 is a view showing an interior structure of a stopper accordingto a modification of the present invention;

FIG. 12 is a view of an interior reinforcing structure of the stopperaccording to the modification of the present invention;

FIG. 13 is a longitudinal sectional view of the stopper in a lockedstate, according to the modification of the present invention; and

FIG. 14 is a longitudinal sectional view of the stopper in an unlockedstate, according to the modification of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

Referring to the accompanying drawings, the present invention is anapparatus for vertical movement and height adjustment of a derrickdesigned to support a drilling pipe during drilling operation. However,it should be understood that the present invention can also be appliedto any structure including a mast as well as the derrick so long as thestructure is capable of supporting the drilling pipe during not onlyoverland but also offshore drilling operation.

Referring to FIG. 3 to FIG. 10, a derrick lift system of an offshorestructure according to one embodiment of the present invention is placedon a drill floor 14 and includes base plates 110 each having a lockinggroove 110 a on one side thereof

Each of the base plates 110 is provided at one inner side thereof with agearbox 120, which is coupled to a hydraulic drive motor 121. Thegearbox 120 refers to a unit of gears for power transmission and is wellknown in the art. Thus, a detailed description of the gearbox is omittedherein.

A relay gear 130 is rotatably mounted on the base plate 110 to engagewith the gearbox 120.

A pinion 140 is rotably mounted on the base plate 110 to engage with therelay gear 130.

A post 150 is provided to the other inner side of each of the baseplates 110 to be perpendicularly movable and supports a lower end of thederrick 100 to move the derrick 100 up or down.

The post 150 has a rack 151 formed on one surface thereof to engage withthe pinion 140 and a locking groove 150 a formed on one side thereof

A stopper 160 is mounted on the base plate 110 to secure the post 150 ata predetermined location.

A derrick height adjustment unit 190 is placed at one side of the baseplate 110 to align the locking grooves 110 a, 150 a through heightadjustment of the derrick 100.

The derrick height adjustment unit 190 includes a mounting bracket 191secured to the base plate 110, and a hydraulic cylinder 192 provided tothe mounting bracket 191 and adjusting the height of the derrick 100.

The hydraulic cylinder 192 may be composed of a hydraulic cylinder body192 a secured to the mounting bracket 191 and a rod 192 b moved in avertical direction by hydraulic pressure to adjust the height of thederrick 100.

The base plate 110 may be provided with a sensor 193 (see FIG. 3) thatdetects alignment of the locking grooves 110 a, 150 a. The pinion 140includes a securing pin 142 that engages with the rack 151.

The base plate is provided with a ratchet cylinder 170, and the ratchetcylinder 170 includes a rod 170 a and a pivot latch 171 rotablyinstalled at the rod.

The pivot latch 171 stops a latch jaw 143 of the pinion 140 selectivelyand latches the pinion 140 not to be rotated.

In other words, when the pinion 140 is rotated in a direction in whichthe post 150 is raised, the pivot latch 171 does not obstruct rotationof the pinion 140. Conversely, when the pinion 140 is rotated in theopposite direction, the pivot latch 171 regulates rotation of the pinion140. That is, the pivot latch 171 is configured to restrict rotation ofthe pinion 140 in order to prevent an accident due to damage to ahydraulic line in a state that the derrick 100 is raised to apredetermined height.

The base plate 110 is provided with a safety cylinder 180 coupled to thestopper 160 to selectively lock the stopper 160. The safety cylinder 180serves to lock the stopper 160.

The base plates 110 and the posts 150 may be arranged to support fourlower corners of the derrick 100.

The derrick lift system according to this embodiment may lift thederrick 100 through engagement between the rack 151 and the pinion 140after receiving power from the drive motor 121, and may adjust theheight of the derrick 100 through the derrick height adjustment unit190.

The base plates 110 are secured to the drill floor 14. The post 150 isplaced at the other inner side of each of the base plates 110 to beperpendicularly movable and to support the lower end of the derrick 100so as to lift or lower the derrick 100.

The sensor 193 detects alignment between the locking groove 110 a of thebase plate 110 and the locking groove 150 a of the post 150, andautomatically activates the stopper 160 to secure the location of thederrick 100.

Next, operation of the derrick lift system of an offshore structure withthe aforementioned configuration will be described.

The derrick 100 is lowered to lower the center of gravity of the derrickwhen a drill ship is moved to a drilling point or rerouted to avoidaccident due to a typhoon and the like, whereas the derrick 100 islifted upon drilling operation.

In operation of lifting the derrick 100, the drive motor 121 engagingwith the gearbox 120 is driven to rotate the relay gear 130 engagingwith gearbox 120, thereby rotating the pinion 140 engaging with therelay gear 130.

Since the rack 150 engages with the securing pin 142 of the pinion 140,the rack 150 is raised through rotation of the pinion 140. Here, thepost 110 integrally formed with the rack 150 is also raised, whereby thederrick 100 provided to the post 110 is raised.

Then, since the stopper 160 is inserted into the locking grooves 110 a,150 a in order to secure the post 150 in a lifted or lowered state, itis necessary to adjust the height of the derrick 100. However, since thederrick 100 is very heavy, it is difficult to achieve accurate heightadjustment of the derrick 100. Moreover, even in the case where theheight of the derrick 100 is accurately adjusted, the derrick 100 islikely to sag due to heavy weight thereof over time.

As such, non-accurate height adjustment of the derrick 100 causesmisalignment of the locking grooves 110 a, 150 a, whereby the stopper160 cannot be inserted into and locked to the locking grooves 110 a, 150a. Accordingly, work is very difficult in an actual work site sinceleveling operation (height adjustment) of the derrick 100 is repeatedseveral times. However, according to the present invention, the heightof the derrick 100 can be easily adjusted using the derrick heightadjustment unit 190. That is, according to the present invention, thederrick height adjustment unit 190 is driven to lift and gradually lowerthe derrick 100 such that the height of the derrick can be set to adesired location to align the locking grooves 110 a, 150 a, whereby thestopper 160 can be easily and conveniently inserted into the lockinggrooves 110 a, 150 a and locked thereby.

On the other hand, although alignment of the locking grooves 110 a, 150a can be confirmed by an operator with the naked eye, the sensor 193 maybe used to confirm alignment of the locking grooves 110 a, 150 a. Whenthe sensor 193 is used to confirm alignment of the locking grooves, itis possible to improve operation safety and accuracy.

In addition, after detecting alignment between the locking grooves 110a, 150 a, the sensor 193 sends a detection signal to a controller (notshown), which in turn automatically operates the stopper 160 to lock thelocation of the derrick 100. In this way, a series of procedures oflifting, leveling and locking the derrick 100 can be realized in anautomatic manner.

Next, a stopper according to a modification of the present inventionwill be described with reference to FIG. 11 to FIG. 14.

The derrick 100 is disposed to be lifted or lowered, and a stopper 260is provided to lock the derrick 100 at a lifted or lowered location.Here, the stopper 260 may include a stationary rod 262 and a cylinderbody 263 moved along the rod 262. In this modification, the stopper 260is configured to allow the cylinder body 263 to be moved into and lockedby the locking grooves 110 a, 150 a, unlike the stopper 160 describedabove. As such, when the cylinder body 263 is moved into and locked bythe locking grooves 110 a, 150 a, the stopper can exhibit high enduranceto high load of the derrick without deformation.

Now, the configuration of the stopper 260 will be described in moredetail. The stopper 260 includes a guide plate 261 secured to a sidesurface of the base plate 110 and having a guide rail 261 b formed on anupper surface thereof; the rod 262 horizontally secured above the guideplate 261; a cylinder body 263 disposed to receive the rod 262 thereinand to be locked into the locking grooves 110 a, 150 a while movingalong the rod 262 by hydraulic force and having safety grooves 263 fformed on upper surfaces of both ends thereof; and a safety cylinder 264secured to a side surface of the base plate 110 and coupled into thesafety grooves 263 f to prevent separation of the cylinder body 263 fromthe locking grooves 110 a, 150 a when the cylinder body 263 is insertedinto the locking grooves 110 a, 150 a.

After alignment of the locking grooves 110 a, 150 a, the stopper 260 isinserted into (locked to) the locking grooves 110 a, 150 a in thefollowing manner. When alignment between the locking grooves 110 a, 150a is confirmed, hydraulic pressure is supplied into the cylinder body263 and forces the cylinder body 263 to be inserted into the lockinggrooves 110 a, 150 a while moving along the rod 262. Here, the guiderail 261 b enables smooth movement of the cylinder body 263. Then, thesafety cylinder 264 is coupled (locked) into the safety grooves 263 f,whereby locking of the stopper 260 can be safely and rigidly maintained.

As described above, since the derrick 100 is composed of a heavystructure having a high load, the load of the derrick 100 is transferredto the cylinder body 263. At this time, as compared with a typicalhydraulic cylinder, the cylinder body 263 can sufficiently endure theload of the derrick 100 through a thick outer plate 263 d and areinforcing lattice 263 e of the cylinder body 263, thereby providingsignificantly improved locking performance

As described above, the derrick lift system of an offshore structureaccording to the embodiments of the present invention can improvedrilling workability by enabling safe and easy height adjustment of thederrick using the adjustment unit, and can improve structural stabilityby lowering the center of gravity of the derrick through the heightadjustment of the derrick, as occasion demands.

Although some embodiments have been described above, it will be apparentto those skilled in the art that these embodiments are given by way ofillustration only, and that various modifications, changes, alterations,and equivalent embodiments can be made without departing from the spiritand scope of the invention. The scope of the invention should be limitedonly by the accompanying claims.

What is claimed is:
 1. A derrick lift system of an offshore structure,comprising: a base plate secured to a drill floor and having a lockinggroove formed on one side thereof; a gearbox placed at one inner side ofthe base plate and coupled to a drive motor; a relay gear rotablymounted on the base plate to engage with the gearbox; a pinion rotablymounted on the base plate to engage with the relay gear; a postsupporting a lower end of the derrick to lift or lower the derrick andprovided to the other inner side of the base plate to be perpendicularlymovable, the post having a rack formed on one surface thereof to engagewith the pinion and a locking groove formed on one side thereof; astopper mounted on the base plate and selectively inserted into thelocking grooves to secure the post at a lifted or lowered location; anda derrick height adjustment unit placed at one side of the base plate toalign the locking grooves through height adjustment of the derrick. 2.The derrick lift system of an offshore structure according to claim 1,wherein the derrick height adjustment unit comprises: a mounting bracketsecured to the base plate; and a hydraulic cylinder provided to themounting bracket and adjusting the height of the derrick.
 3. The derricklift system of an offshore structure according to claim 1, wherein thebase plate is provided with a sensor detecting alignment of the lockinggrooves.
 4. The derrick lift system of an offshore structure accordingto claim 1, wherein the pinion comprises a securing pin engaging withthe rack, and the base plate is provided with a safety cylinder coupledto the stopper to selectively lock the stopper.
 5. The derrick liftsystem of an offshore structure according to claim 4, wherein the baseplate is provided with a ratchet cylinder, the ratchet cylindercomprising a rod and a pivot latch latched to a latch jaw of the pinionthrough the rod of the ratchet cylinder.
 6. The derrick lift system ofan offshore structure according to claim 1, wherein the base plate andthe post are arranged to support four lower corners of the derrick. 7.The derrick lift system of an offshore structure according to claim 1,wherein the stopper comprises: a guide plate secured to a side surfaceof the base plate and having a guide rail formed on an upper surfacethereof; a rod horizontally secured above the guide plate; a cylinderbody disposed to receive the rod therein and to be locked into thelocking grooves while moving along the rod by hydraulic force, andhaving safety grooves formed on upper surfaces of both ends thereof; anda safety cylinder secured to a side surface of the base plate andcoupled into the safety grooves to prevent separation of the cylinderbody from the locking grooves when the cylinder body is inserted intothe locking grooves.
 8. The derrick lift system of an offshore structureaccording to claim 7, wherein the cylinder body is formed with fluidinlet and outlet ports and a hydraulic chamber, and has safety groovesformed on upper surfaces of both ends thereof